It is desirable to be able to sense the temperature of a semiconductor element for a variety of purposes. For instance, it is a problem with many sorts of semiconductor element that overheating of the element may, if prolonged, lead to the destruction of that element. By way of example, any MOS (metal oxide semiconductor) switch has a limit to its capability to dissipate power which, if exceeded, may result in the overheating and self-destruction of the MOS switch. The power dissipated by a switch is the product of the voltage across the switch and the current through the switch: the switch is normally used in conjunction with a load which, under normal operating conditions, limits the current through the switch and the voltage across it to a value within the power dissipation capability of the switch. Should the load be inadvertently short circuited, the total supply voltage will be across the switch which may result in the power dissipation capability being exceeded with consequent overheating and destruction of the switch.